Cutting insert and milling tool

ABSTRACT

A cutting insert includes a first end surface and a second end surface, in which a first peripheral side surface includes a first rake surface adjacent to a first main cutting edge and a first concave surface connected to the second end surface and formed to be recessed from the first rake surface toward a central axis of a through hole, and the first concave surface has a first restraint surface provided at a position where a distance between the first restraint surface and a second main cutting edge is smaller than a distance between the central axis of the through hole and the second main cutting edge, when viewed from a direction parallel to the central axis of the through hole.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application relates to and claims priority from Japanese PatentApplication No. 2019-190864 on (Oct. 18, 2019), the entire disclosure ofwhich is incorporated herein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present disclosure relates to a cutting insert and a milling tool.

Description of Related Art

In the related art, a cutting insert that can achieve both lowresistance and high rigidity when vertically placed has been known.

International Publication No. 2017/068922 and International PublicationNo. 2011/013115 disclose such a cutting insert and a milling toolmounted on the cutting insert. Further, Kyocera Corporation, “HighPerformance End Mill MEV”, October 2019, Internet<https://www.kyocera.co.jp/prdct/tool/wp-content/uploads/2019/09/MEV.pdf>discloses an end mill having both low resistance and high rigidity.

When being mounted on a body, such a cutting insert has a large lengthin a circumferential direction with reference to a rotation axis of thebody. Therefore, the cutting insert is supported by the body at aposition separated from a cutting edge by a distance corresponding tothe thickness of the cutting insert.

The inventors of the present application have focused on a problem thatwhen the cutting insert is supported by the body at a position far awayfrom the cutting edge, a large load is applied to a screw for fixing thecutting insert to the body, and thus a cutting edge position is notstable.

SUMMARY

The purpose of the present disclosure is to provide a cutting insert anda milling tool capable of stabilizing a cutting edge position even whena load is applied to a cutting edge.

A cutting insert according to an aspect of the present disclosure mayinclude a first end surface and a second end surface. Further, a throughhole may be formed to penetrate the first end surface and the second endsurface. The cutting insert may further include: a first peripheral sidesurface connected to the first end surface and the second end surface; asecond peripheral side surface which is connected to the first endsurface, the second end surface, and the first peripheral side surface,and is formed to be rotationally symmetric to the first peripheral sidesurface with respect to a central axis of the through hole; a thirdperipheral side surface which is connected to the first end surface, thesecond end surface, and the second peripheral side surface, and isformed to be rotationally symmetric to the second peripheral sidesurface with respect to the central axis of the through hole; a firstmain cutting edge formed at a connection portion between the first endsurface and the first peripheral side surface; a second main cuttingedge formed at a connection portion between the first end surface andthe second peripheral side surface; and a third main cutting edge formedat a connection portion between the first end surface and the thirdperipheral side surface. Further, the first peripheral side surface mayinclude a first rake surface adjacent to the first main cutting edge,and a first concave surface which is connected to the second end surfaceand is formed to be recessed from the first rake surface toward thecentral axis of the through hole, the first concave surface has a firstrestraint surface provided at a position where a distance between thefirst restraint surface and the second main cutting edge is smaller thana distance between the central axis of the through hole and the secondmain cutting edge when viewed from a direction parallel to the centralaxis of the through hole, the second peripheral side surface has asecond concave surface and a second restraint surface formed to berotationally symmetric to the first concave surface and the firstrestraint surface with respect to the central axis of the through hole,respectively, and the third peripheral side surface has a third concavesurface and a third restraint surface formed to be rotationallysymmetric to the second concave surface and the second restraint surfacewith respect to the central axis of the through hole, respectively.

According to such a configuration, when cutting is performed using thesecond main cutting edge, it is possible to support the cutting insertusing the first concave surface provided on the first peripheral sidesurface corresponding to the first main cutting edge. The first concavesurface has the first restraint surface provided at a position where adistance between the first restraint surface and the second main cuttingedge is smaller than a distance between the central axis of the throughhole and the second main cutting edge, when viewed from the directionparallel to the central axis of the through hole. Therefore, bysupporting the cutting insert using the first restraint surface, it ispossible to reduce a moment acting on the first restraint surface. Asthe distance between the first restraint surface and the second maincutting edge becomes smaller when viewed from the direction parallel tothe central axis of the through hole, the moment acting on the firstrestraint surface can become smaller. Thus, it is preferable that thisdistance be a half or less of the distance between the central axis ofthe through hole and the second main cutting edge when viewed from thedirection parallel to the central axis of the through hole. However, itshould be noted that when the distance between the first restraintsurface and the second main cutting edge is made too small, the rigidityis reduced.

Here, the distance between the central axis of the through hole and thesecond main cutting edge when viewed from the direction parallel to thecentral axis of the through hole is the minimum distance between thecentral axis of the through hole and the second main cutting edge whenviewed from the direction parallel to the central axis of the throughhole. However, the second main cutting edge is not necessarily astraight line. Further, the distance between the first restraint surfaceand the second main cutting edge when viewed from the direction parallelto the central axis of the through hole is the minimum distance betweenthe first restraint surface and the second main cutting edge when viewedfrom the direction parallel to the central axis of the through hole. Thefirst restraint surface may have a flat surface portion, but may beconfigured by a curved surface.

Further, the second peripheral side surface may be formed to berotationally symmetric to the first peripheral side surface by 120degrees, the third peripheral side surface may be formed to berotationally symmetric to the second peripheral side surface by 120degrees, and the first peripheral side surface may be formed to berotationally symmetric to the third peripheral side surface by 120degrees.

According to such a configuration, when the cutting is performed usingthe second main cutting edge, it is possible to support the cuttinginsert by using the first restraint surface of the first concave surfaceand the third concave surface. Further, when the cutting is performedusing the third main cutting edge, it is possible to support the cuttinginsert by using the second restraint surface of the second concavesurface and the first concave surface. Further, when the cutting isperformed using the first main cutting edge, it is possible to supportthe cutting insert by using the third restraint surface of the thirdconcave surface and the second concave surface.

Further, the cutting insert may further include: a first sub-cuttingedge formed at a connection portion between the first peripheral sidesurface and the second peripheral side surface; a second sub-cuttingedge formed at a connection portion between the second peripheral sidesurface and the third peripheral side surface; and a third sub-cuttingedge formed at a connection portion between the third peripheral sidesurface and the first peripheral side surface.

According to such a configuration, since a bottom surface, a wallsurface, and the like can be simultaneously cut using the main cuttingedge and the sub-cutting edge, the cutting insert which can bepreferably used for a milling tool such as a milling cutter and an endmill can be provided.

A corner cutting edge that connects the main cutting edge and thesub-cutting edge may be provided between the main cutting edge and thesub-cutting edge. As in a cutting insert for a radius end mill, thecorner cutting edge may have a large radius of curvature. Further, thesub-cutting edge may be provided such that a ramping process can beperformed.

The first concave surface may have a first sub-restraint surfaceprovided at a position where a distance between the first sub-restraintsurface and the second main cutting edge is larger than the distancebetween the central axis of the through hole and the second main cuttingedge when viewed from the direction parallel to the central axis of thethrough hole, the second concave surface may have a second sub-restraintsurface formed to be rotationally symmetric to the first sub-restraintsurface with respect to the central axis of the through hole, and thethird concave surface may have a third sub-restraint surface formed tobe rotationally symmetric to the second sub-restraint surface withrespect to the central axis of the through hole.

According to such a configuration, when the cutting is performed usingthe second main cutting edge, the cutting insert can be supported usingthe first restraint surface of the first concave surface and the thirdsub-restraint surface of the third concave surface. Further, the cuttinginsert can be supported using the third restraint surface of the thirdconcave surface and the second sub-restraint surface of the secondconcave surface when the cutting is performed using the first maincutting edge or using the second restraint surface of the second concavesurface and the first sub-restraint surface of the first concave surfacewhen the cutting is performed using the third main cutting edge.

Further, the first concave surface may have a first bottom surfacefacing the same direction as the second end surface, and a first wallsurface standing up from the first bottom surface and connected to thesecond end surface, the first wall surface may have the first restraintsurface, the first restraint surface may have a first flat surfaceportion, and an angle formed between the first flat surface portion andthe second main cutting edge may be −40 degrees or more and 40 degreesor less when viewed from a direction parallel to the central axis of thethrough hole.

With such a configuration, since the first restraint surface is asurface facing a direction in which the cutting insert rotates, it ispossible to preferably receive the cutting resistance acting on thesecond main cutting edge. Further, since an angle formed between thefirst flat surface portion and the second main cutting edge is −40degrees or more and 40 degrees or less, as compared to a case where theangle has any other value, it is possible to preferably receive thecutting resistance acting in a direction perpendicular to a rotationaxis of the body when viewed from the direction parallel to the centralaxis of the through hole.

Further, when viewed from the direction parallel to the central axis ofthe through hole, the first flat surface portion may be formed to becloser to the second main cutting edge as the first flat surface portionis farther from the first main cutting edge.

According to such a configuration, when the cutting insert is attachedto the body such that the second main cutting edge has a positive axialrake, it is possible to make the first restraint surface rather than thesecond main cutting edge approach the rotation axis of the body inparallel to the rotation axis of the body. Therefore, when viewed fromthe direction parallel to the central axis of the through hole, it ispossible to preferably receive the cutting resistance acting in thedirection perpendicular to the rotation axis of the body.

Further, the first wall surface may have a first sub-restraint surface,the first sub-restraint surface may have a first sub-flat surfaceportion, and when viewed from a direction facing the second end surfaceparallel to the central axis of the through hole, an angle of the firstsub-flat surface portion with respect to the first flat surface portionmay be 0 degrees or more and 90 degrees or less.

According to such a configuration, when the cutting is performed usingthe second main cutting edge, the cutting insert can be supported usingthe first restraint surface of the first concave surface and the thirdsub-restraint surface of the third concave surface. In particular, ifthe first concave surface and the third concave surface are provided tobe rotationally symmetric to each other by 120 degrees, when viewed fromthe direction facing the second end surface parallel to the central axisof the through hole, an angle between the third sub-restraint surfaceand the second main cutting edge can be 0 degrees or more and 90 degreesor less. Therefore, the cutting insert can be stably supported incooperation with the first sub-restraint surface of the first concavesurface. Similarly, the cutting insert can be stably supported using thethird restraint surface of the third concave surface and the secondsub-restraint surface of the second concave surface when the cutting isperformed using the first main cutting edge or using the secondrestraint surface of the second concave surface and the firstsub-restraint surface of the first concave surface when the cutting isperformed using the third main cutting edge.

Further, a milling tool according to an aspect of the present disclosuremay include such a cutting insert, and a body which rotates about arotation axis and to which the cutting insert is attached.

According to such a milling tool, even when a load is applied to thecutting edge, the cutting edge position can be stabilized.

Further, the cutting insert attached to the body that rotates about therotation axis may include a first end surface facing an outer diameterdirection when attached to the body and a second end surface facing aninner diameter direction when attached to the body, in which a throughhole penetrating the first end surface and the second end surface isformed, the cutting insert further includes a first peripheral sidesurface that connects the first end surface and the second end surfaceand faces a rotation direction when attached to the body, a first maincutting edge formed at a connection portion between the first peripheralside surface and the first end surface, and a second peripheral sidesurface that connects the first end surface and the second end surfaceand faces a rotation axis direction from a base end to a tip of the bodywhen attached to the body, and the second peripheral side surface mayhave a concave surface that is recessed toward a central axis of thethrough hole and is provided with a first restraint surface such that adistance between the first restraint surface and the first main cuttingedge is smaller than a distance between the central axis of the throughhole and the first main cutting edge when viewed from the directionparallel to the central axis of the through hole.

Further, the cutting insert may include a second main cutting edgeformed at a connection portion between the second peripheral sidesurface and the first end surface, a third peripheral side surfaceconnecting the first end surface and the second end surface, and a thirdmain cutting edge formed at a connection portion between the thirdperipheral side surface and the first end surface, in which the firstmain cutting edge, the second main cutting edge, and the third maincutting edge are formed to be rotationally symmetric to the central axisof the through hole by 120 degrees, and the first peripheral sidesurface, the second peripheral side surface having the concave surface,and the third peripheral side surface are formed to be rotationallysymmetric to the central axis of the through hole by 120 degrees.

Further, the concave surface may be connected to the second end surface,and the area of the first end surface may be larger than the area of thesecond end surface.

Further, the cutting insert may further include a first sub-cutting edgeformed at a connection portion between the first peripheral side surfaceand the second peripheral side surface, and a first corner cutting edgeconnected to the first sub-cutting edge and the first main cutting edge.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a cutting insert when viewed from afirst end surface side.

FIG. 2 is a perspective view of the cutting insert when viewed from asecond end surface side.

FIG. 3 is a plan view of the cutting insert.

FIG. 4 is a left side view of the cutting insert.

FIG. 5 is a rear view of the cutting insert.

FIG. 6 is a perspective view of a milling cutter.

FIG. 7 is a perspective view of a body.

DETAILED DESCRIPTION

Embodiments of the present disclosure will be described below withreference to the drawings. The following embodiments are examples forexplaining the present disclosure, and are not intended to limit thepresent disclosure only to the embodiments.

FIG. 1 is a perspective view of a cutting insert 10 according to theembodiment when viewed from a first end surface 12 side. FIG. 2 is aperspective view of the cutting insert 10 when viewed from a second endsurface 14 side. Further, FIGS. 3 to 5 are a plan view, a left sideview, and a rear view of the cutting insert 10, respectively.

The first end surface 12 of the cutting insert 10 has a surfacefunctioning as flanks of a first main cutting edge 18A, a second maincutting edge 18B, and a third main cutting edge 18C. The first endsurface 12 is formed, for example, in a triangular shape, and includesthree corner portions corresponding to the vertices and three sidesconnecting the vertices. The second end surface 14 (FIG. 2) is formed ina direction opposite to the first end surface 12. Further, the cuttinginsert 10 is provided with a through hole H penetrating the center ofthe first end surface 12 and the center of the second end surface 14. Acentral axis AX (FIG. 3) of the through hole H is substantiallyperpendicular to the first end surface 12 and the second end surface 14.

The cutting insert 10 is formed rotationally symmetrically with respectto the central axis AX of the through hole H by 120 degrees. Therefore,a first peripheral side surface 16A, a second peripheral side surface16B, and a third peripheral side surface 16C are formed rotationallysymmetrically to each other by 120 degrees. Similarly, a first maincutting edge 18A, a second main cutting edge 18B, and a third maincutting edge 18C and a first sub-cutting edge 20A, a second sub-cuttingedge 20B, and a third sub-cutting edge 20C are formed rotationallysymmetrically to each other by 120 degrees, respectively, and includethe same structure.

The first peripheral side surface 16A is connected to the first endsurface 12 and the second end surface 14 at an end portion in adirection of the central axis AX. Further, the first peripheral sidesurface 16A is connected to the second peripheral side surface 16B andthe third peripheral side surface 16C at a circumferential end portionwith reference to the central axis AX. Further, the first main cuttingedge 18A, the second main cutting edge 18B, and the third main cuttingedge 18C are formed in connection portions between the first end surface12, the first peripheral side surface 16A, the second peripheral sidesurface 16B, and the third peripheral side surface 16C, respectively.

Further, the first sub-cutting edge 20A is formed at a connectionportion between the first peripheral side surface 16A and the thirdperipheral side surface 16C, the third sub-cutting edge 20C is formed ata connection portion between the third peripheral side surface 16C andthe second peripheral side surface 16B, and the second sub-cutting edge20B is formed at a connection portion between the second peripheral sidesurface 16B and the first peripheral side surface 16A.

Further, a first corner cutting edge 22A formed in a circular arc shapeor an arc shape to be connected to the first main cutting edge 18A atone end and the first sub-cutting edge 20A at the other end is formed ata corner portion connecting the first main cutting edge 18A and thefirst sub-cutting edge 20A. However, the curvature of the first cornercutting edge 22A may not be constant, and for example, the curvature maybe configured to gradually increase or decrease partially or entirely soas to be connected to the first main cutting edge 18A or the firstsub-cutting edge 20A. Similarly, a corner cutting edge 22B and a cornercutting edge 22C are formed to be rotational symmetric to the firstcorner cutting edge 22A.

As illustrated in FIGS. 1 and 2, the first peripheral side surface 16Aincludes a first rake surface 24A adjacent to the first main cuttingedge 18A, the first sub-cutting edge 20A, and the first corner cuttingedge 22A, a first concave surface 26A formed to be recessed from thefirst rake surface 24A toward the central axis AX of the through hole H,and a flank of the second sub-cutting edge 20B formed adjacent to thesecond sub-cutting edge 20B.

The first concave surface 26A has a first bottom surface 26A1 connectedto the first rake surface 24A and formed in the same direction as thesecond end surface 14 (FIGS. 2 and 5) and a first wall surface 26A2standing up from the first bottom surface 26A1 and connected to thesecond end surface 14. As illustrated in FIGS. 2 and 5, the first wallsurface 26A2 includes a first restraint surface 26A21 and a firstsub-restraint surface 26A22.

The first restraint surface 26A21 is a surface that can restrainmovement of the cutting insert 10 with respect to a body 50 by abuttingon and being supported by the body 50 when cutting is performed with thesecond main cutting edge 18B as a cutting edge.

As illustrated in FIG. 5, when the cutting insert 10 is viewed from adirection facing the second end surface 14 which is a direction parallelto the central axis AX of the through hole H, a distance between thefirst restraint surface 26A21 and the second main cutting edge 18B issmaller than a distance (the minimum length of a line segment connectingthe two members. The same manner is applied to the following) betweenthe central axis AX of the through hole H and the second main cuttingedge 18B. Therefore, when the cutting is performed with the second maincutting edge 18B as a cutting edge, it is possible to preferably receivecutting resistance acting on the second main cutting edge 18B. Withrespect to a distance of a line segment connecting the first restraintsurface 26A21 and the second main cutting edge 18B, since the smallerdistance can exhibit a function as a restraint surface within a range inwhich rigidity can be maintained, the first restraint surface 26A21 isformed such that the distance is preferably 70% or less of the distancebetween the central axis AX of the through hole H and the second maincutting edge 18B, and is further preferably 50% or less of the distancebetween the central axis AX of the through hole H and the second maincutting edge 18B. However, this does not prevent a part, for example, aperipheral part, of the first restraint surface 26A21, from having aregion outside the above range.

The first restraint surface 26A21 is formed to include, for example, aflat surface portion (an example of a “first flat surface portion”)substantially parallel to the central axis AX of the through hole H. Inthat case, as illustrated in FIG. 5, it is possible to draw a straightline L1 passing through the flat surface portion of the first restraintsurface 26A21. On the other hand, the second main cutting edge 18B isformed to have, for example, a linear shape when viewed from a directionparallel to the central axis AX of the through hole H. In this case, asillustrated in the drawing, it is possible to draw a straight line L2that approximates the second main cutting edge 18B. When viewed from adirection parallel to the central axis AX of the through hole H, forexample, the flat surface portion of the first restraint surface 26A21is formed to be closer to the second main cutting edge 18B as the flatsurface portion is farther from the first main cutting edge 18A. Withsuch a configuration, when the cutting is performed using the secondmain cutting edge 18B, if the cutting insert 10 is attached to the body50 such that an axial rake becomes positive, an angle formed between theflat surface portion of the first restraint surface 26A21 and an axialdirection of a rotation axis of the body 50 can be closer to a parallelstate, as compared to a case where the flat surface portion of the firstrestraint surface 26A21 is provided parallel to the first main cuttingedge 18A. Therefore, the flat surface portion of the first restraintsurface 26A21 can preferably receive cutting resistance acting in adirection perpendicular to the rotation axis of the body 50.

However, the angle formed between the flat surface portion of the firstrestraint surface 26A21 is not limited to the above, the flat surfaceportion may be formed such that an angle a (FIG. 5) of the straight lineL1 with reference to the straight line L2 is more than −60 degrees andless than 60 degrees, the flat surface portion may be formed such thatthe angle a is preferably −40 degrees or more and 40 degrees or less,and the flat surface portion may be formed such that the angle a is morepreferably 0 degrees or more and −10 degrees or less. FIG. 5 illustratesa case where the angle a is −10 degrees or less. In FIG. 5, the angle ofthe straight line L1 with reference to the straight line L2 isdetermined such that the angle of the straight line L1 with respect tothe straight line L2 is positive in a counterclockwise direction and isnegative in a clockwise direction. Further, the first restraint surface26A21 may be configured by only a curved surface or a flat surface and acurved surface. For example, the first restraint surface 26A21 may havea curved surface at an end portion of the flat surface portion, and maybe configured such that even a curved surface portion can abut on thebody 50. In the present embodiment, the first restraint surface 26A21 isconfigured to be visible from the second end surface 14. However, thepresent disclosure is not limited thereto. Even when the first restraintsurface 26A21 cannot be seen from the second end surface 14, a surfaceof the first concave surface 26A corresponding to the first restraintsurface 26A21 can be configured in the same manner as described above.For example, the cutting insert may be provided to have the sameconfiguration in a cross section perpendicular to the central axis AX ofthe through hole H.

The first sub-restraint surface 26A22 is a surface which can restrainmovement of the cutting insert 10 with respect to the body 50 byabutting on and being supported by the body 50 when the cutting isperformed with the third main cutting edge 18C as a cutting edge.

As illustrated in FIG. 5, when the cutting insert 10 is viewed from adirection facing the second end surface 14 that is a direction parallelto the central axis AX of the through hole H, a distance between thefirst sub-restraint surface 26A22 and the second main cutting edge 18Bis larger than a distance between the central axis AX of the throughhole H and the second main cutting edge 18B. On the other hand, adistance between the first sub-restraint surface 26A22 and the thirdmain cutting edge 18C is smaller than a distance between the centralaxis AX of the through hole H and the third main cutting edge 18C.Therefore, when the cutting is performed with the third main cuttingedge 18C as a cutting edge, it is possible to preferably receive thecutting resistance acting on the third main cutting edge 18C. That is,when viewed from a direction parallel to the central axis AX of thethrough hole H, the first concave surface 26A can be used as a restraintsurface when the cutting is performed using the second main cutting edge18B since the first concave surface 26A has the first restraint surface26A21 formed at a position having a smaller distance to the second maincutting edge 18B than the distance between the central axis AX of thethrough hole H and the second main cutting edge 18B, and can be used asa restraint surface when the cutting is performed using the third maincutting edge 18C since the first concave surface 26A has the firstsub-restraint surface 26A22 formed at a position having a smallerdistance to the third main cutting edge 18C than the distance betweenthe central axis AX of the through hole H and the third main cuttingedge 18C.

The first sub-restraint surface 26A22 is formed to include, for example,a flat surface portion (an example of a “first sub-flat surfaceportion”) substantially parallel to the central axis AX of the throughhole H. In that case, as illustrated in FIG. 5, it is possible to draw astraight line L3 passing through the flat surface portion of the firstsub-restraint surface 26A22. It is preferable that an angle b of thestraight line L3 with reference to the straight line L1 be 0 degrees ormore and 90 degrees or less. With this configuration, for example, whenthe cutting is performed using the second main cutting edge 18B, it ispossible to support the cutting insert 10 from two different directionsof the first restraint surface 26A21 and a third sub-restraint surface26C22. The first sub-restraint surface 26A22 may be configured by only acurved surface or a flat surface and a curved surface. For example, thefirst sub-restraint surface 26A22 may have a curved surface at an endportion of the flat surface portion, and may be configured such thateven a curved surface portion can abut on the body 50. In the presentembodiment, the first sub-restraint surface 26A22 is configured to bevisible from the second end surface 14. However, the present disclosureis not limited thereto. Even when the first sub-restraint surface 26A22cannot be seen from the second end surface 14, a surface correspondingto the first sub-restraint surface 26A22 can be configured in the samemanner as described above. For example, the cutting insert may beprovided such that a distance between a projection line of the maincutting edge 18A and a straight line or a curved line constituting thefirst restraint surface 26A21 and the first sub-restraint surface 26A22in a cross section perpendicular to the central axis AX of the throughhole H has the above-described relationship.

The first wall surface 26A2 has a connection surface that connects thefirst restraint surface 26A21 and the first sub-restraint surface 26A22.The connection surface is a surface that faces the surface of the body50 while being apart adjacently when the cutting insert 10 is attachedto the body 50.

The second peripheral side surface 16B and the third peripheral sidesurface 16C have the same configuration that is rotationally symmetricalwith the first peripheral side surface 16A, including the constituentelements such as the second concave surface 26B and the third concavesurface 26C included therein. These constituent elements are given thesame reference numeral except that the beginning thereof is the secondor the third and the alphabet at the end is B or C, and detaileddescription thereof will be omitted.

The action and effect of the cutting insert 10 including theabove-described configuration will be described.

In general, when a vertical cutting insert is mounted on the body, thethickness of the cutting insert, that is, the length in acircumferential direction with reference to the rotation axis of thebody, is large. Therefore, in order to prevent a rotational rear endportion of the cutting insert from colliding with an object to be cut,the cutting insert is often mounted on the body in a state in which aradial rake has a negative value or a value close to a negative value.However, when the radial rake has a negative value or a value close to anegative value and the cutting insert is mounted on the body, if thecutting edge comes into contact with the object to be cut, large cuttingresistance acts in a direction away from the body. Therefore, a largeload is applied to a screw for fixing the cutting insert to the body,and thus it is not easy to stabilize the cutting edge position of thecutting edge. In the related art, the problem is solved by causing themost region of the outer peripheral surface of the cutting insert toabut on the body as a restraint surface.

However, as a result of analysis by the inventors of the presentapplication, it is noted that in the configuration according to therelated art, when a large cutting resistance acts, the cutting edgeposition may deviate from an original position. Further, it is notedthat when the cutting insert is formed in a triangular shape, therotational rear end portion of the cutting insert is pressed against thebody like a wedge and thus it is difficult to take out the cuttinginsert, and since the cutting insert is asymmetric in the verticaldirection, the cutting insert may be displaced downward when beingpressed against the body.

On the other hand, the cutting insert 10 according to the presentembodiment is provided with the first restraint surface 26A21 and thelike that can abut on the body 50 at a position having a smallerdistance to the main cutting edge 18B used for the cutting than adistance between the main cutting edge 18B and the central axis AX ofthe through hole H corresponding to the center of an inscribed circle ofthe cutting insert 10 when viewed from an opposite direction from thefirst end surface 12 or the second end surface 14. Therefore, when thecutting is performed with the main cutting edge 18B as a cutting edge, amoment acting on the first restraint surface 26A21 or the like can besmaller as compared to a case where a restraint surface is provided at aposition separated from the main cutting edge 18B or the like by thesame distance as the distance between the central axis AX of the throughhole H and the main cutting edge 18B. Further, the first restraintsurface 26A21 or the like is provided at a position close to the firstcorner cutting edge 22A and the like of the main cutting edge 18B or thelike. Therefore, when the cutting edge is bitten, since the first cornercutting edge 22A or the like or the vicinity thereof firstly comes intocontact with a cutting material, it is possible to appropriately receivethe cutting resistance at a position where large cutting resistance canbe received. Therefore, as compared to the related art, it is possibleto suppress the positional deviation due to the cutting resistance.

Further, the first restraint surface 26A21 or the like is provided toface the rotational direction of the body 50, that is, to be parallel toor almost parallel to the central axis AX of the through hole H. Thus,the first restraint surface 26A21 and the body 50 can abut on each otherin a direction in which the rigidity of the body 50 is large, so that itis possible to more appropriately suppress the positional deviation.

Further, the cutting insert 10 can be supported by the thirdsub-restraint surface 26C22 or the like provided at a position and anangle different from those of the first restraint surface 26A21 or thelike. In this way, the cutting insert 10 can be supported by one or twoor more surfaces that are independent of the first restraint surface26A21 or the like, so that it is possible to suppress the positionaldeviation due to the cutting resistance. In particular, since the thirdsub-restraint surface 26C22 or the like is provided at a position havinga smaller distance to the main cutting edge 18B used for the cuttingthan a distance between the central axis AX of the through hole H andthe main cutting edge 18B or the like, similarly, the moment acting onthe third sub-restraint surface 26C22 or the like can be reduced.

Further, for example, when the main cutting edge 18B is used for thecutting, the second concave surface 26B is provided on the secondperipheral side surface 16B having a rake surface. Therefore, ascompared with a case where the second concave surface 26B is notprovided, it is possible to suppress the obstruction of chip discharge.In particular, even when the radial rake is made negative, it ispossible to suppress the obstruction of chip discharge.

Further, since the body 50 that supports the cutting insert 10 is formedwith the first concave surface 26A or the like, it is possible toincrease the rigidity in the circumferential direction and in the radialdirection with reference to the rotation axis as compared to a bodyaccording to the related art. As described above, using the cuttinginsert 10, it is possible to increase the rigidity of the body thatsupports the cutting insert 10.

Further, the cutting insert 10 can be configured so as not to abut onthe body on the first end surface 12 side which is a flank of the firstmain cutting edge 18A or the like. Therefore, it is possible to change aclearance angle as compared with a cutting insert that is restrained byabutting on the body on an end surface on the flank side. Therefore, thecutting insert 10 can perform cutting with an optimal clearance angleaccording to various cutting materials and processing purposes. Forexample, it is possible to increase the clearance angle in order toimprove the weldability or to decrease the clearance angle in order toprovide the edge strength.

Further, in the cutting insert 10, the area of the second end surface 14is smaller than the area of the first end surface 12. Therefore, forexample, when the cutting insert 10 is used as an insert for a roughingend mill or the like, the number of edges (the number of attachedcutting inserts 10) can be increased.

The cutting insert 10 can be deformed within a range in which theordinary creativity of those skilled in the art is exhibited. Forexample, a portion that is not related to the present disclosure mayinclude a portion that is not rotationally symmetrical. Further, a landmay be formed adjacent to the first main cutting edge 18A, the secondmain cutting edge 18B, and the third main cutting edge 18C.

Subsequently, a milling cutter 100 including the cutting insert 10 andthe body 50 will be described. FIG. 6 is a perspective view of themilling cutter 100. FIG. 7 is a perspective view of the body 50.

As illustrated in the drawings, a plurality of the cutting inserts 10are attached to the body 50. Further, the cutting insert 10 is pressedagainst the body 50 by a male screw 60 which is inserted through thethrough hole H and screwed into a female screw formed in the body 50. Asillustrated in FIG. 7, a bottom surface 52 abutting on the second endsurface 14, a first jaw portion 54 abutting on the first restraintsurface 26A21 and a second jaw portion 56 abutting on the thirdsub-restraint surface 26C22 when the cutting is performed using thesecond main cutting edge 18B are formed in an attachment part of thecutting insert 10. The length of the body 50 in a circumferentialdirection (rotational direction) with reference to a rotation axis AX2in a portion abutting on the first restraint surface 26A21 by the firstjaw portion 54 is larger than that when the first jaw portion 54 is notformed. Therefore, the rigidity of the body 50 can be increased.Further, it is possible to suppress the positional deviation due to thecutting resistance of the cutting insert 10.

The present disclosure can be variously modified without departing fromthe spirit thereof. For example, the cutting insert 10 may be attachedto the body using a lever inserted into the through hole H. Further, thecutting insert 10 may be used for another milling tool such as an endmill. The present disclosure may be provided for the cutting inserthaving other polygonal shapes such as a quadrangular shape in additionto the triangular shape. Further, within the scope of the ordinarycreativity of those skilled in the art, some of the constituent elementsin the embodiment may be deleted or replaced with other constituentelements.

What is claimed is:
 1. A cutting insert comprising: a first end surface;a second end surface; a through hole being formed to penetrate the firstend surface and the second end surface; a first peripheral side surfaceconnected to the first end surface and the second end surface; a secondperipheral side surface which is connected to the first end surface, thesecond end surface, and the first peripheral side surface, and is formedto be rotationally symmetric to the first peripheral side surface withrespect to a central axis of the through hole; a third peripheral sidesurface which is connected to the first end surface, the second endsurface, and the second peripheral side surface, and is formed to berotationally symmetric to the second peripheral side surface withrespect to the central axis of the through hole; a first main cuttingedge formed at a connection portion between the first end surface andthe first peripheral side surface; a second main cutting edge formed ata connection portion between the first end surface and the secondperipheral side surface; and a third main cutting edge formed at aconnection portion between the first end surface and the thirdperipheral side surface, wherein the first peripheral side surfaceincludes a first rake surface adjacent to the first main cutting edge,and a first concave surface which is connected to the second end surfaceand is formed to be recessed from the first rake surface toward thecentral axis of the through hole, the first concave surface has a firstrestraint surface provided at a position where a distance between thefirst restraint surface and the second main cutting edge is smaller thana distance between the central axis of the through hole and the secondmain cutting edge when viewed from a direction parallel to the centralaxis of the through hole, the second peripheral side surface has asecond concave surface and a second restraint surface formed to berotationally symmetric to the first concave surface and the firstrestraint surface with respect to the central axis of the through hole,respectively, the third peripheral side surface has a third concavesurface and a third restraint surface formed to be rotationallysymmetric to the second concave surface and the second restraint surfacewith respect to the central axis of the through hole, respectively,wherein the first concave surface has a first bottom surface facing thesame direction as the second end surface, and a first wall surfacestanding up from the first bottom surface and connected to the secondend surface, the first wall surface has the first restraint surface, thefirst restraint surface has a first flat surface portion, and an angleformed between the first flat surface portion and the second maincutting edge is −40 degrees or more and 40 degrees or less when viewedfrom the direction parallel to the central axis of the through hole. 2.The cutting insert according to claim 1, wherein the second peripheralside surface is formed to be rotationally symmetric to the firstperipheral side surface by 120 degrees, the third peripheral sidesurface is formed to be rotationally symmetric to the second peripheralside surface by 120 degrees, the first peripheral side surface is formedto be rotationally symmetric to the third peripheral side surface by 120degrees, and the cutting insert further comprises a first sub-cuttingedge formed at a connection portion between the first peripheral sidesurface and the second peripheral side surface, a second sub-cuttingedge formed at a connection portion between the second peripheral sidesurface and the third peripheral side surface, and a third sub-cuttingedge formed at a connection portion between the third peripheral sidesurface and the first peripheral side surface.
 3. The cutting insertaccording to claim 1, wherein the first concave surface has a firstsub-restraint surface provided at a position where a distance betweenthe first sub-restraint surface and the second main cutting edge islarger than the distance between the central axis of the through holeand the second main cutting edge when viewed from the direction parallelto the central axis of the through hole, the second concave surface hasa second sub-restraint surface formed to be rotationally symmetric tothe first sub-restraint surface with respect to the central axis of thethrough hole, and the third concave surface has a third sub-restraintsurface formed to be rotationally symmetric to the second sub-restraintsurface with respect to the central axis of the through hole.
 4. Thecutting insert according to claim 1, wherein when viewed from thedirection parallel to the central axis of the through hole, the firstflat surface portion is formed to be closer to the second main cuttingedge as the first flat surface portion is farther from the first maincutting edge.
 5. The cutting insert according to claim 1, wherein thefirst wall surface has a first sub-restraint surface provided at aposition where a distance between the first sub-restraint surface andthe second main cutting edge is larger than the distance between thecentral axis of the through hole and the second main cutting edge, whenviewed from the direction parallel to the central axis of the throughhole, the first sub-restraint surface has a first sub-flat surfaceportion, and when viewed from a direction facing the second end surfaceparallel to the central axis of the through hole, an angle of the firstsub-flat surface portion with respect to the first flat surface portionis 0 degrees or more and 90 degrees or less.
 6. A milling toolcomprising: the cutting insert according to claim 1; and a body whichrotates about a rotation axis and to which the cutting insert isattached.